Mirrors are simple sheets of glass that have been coated on the backside with aluminum oxide.

This is a process that has been around for hundreds of years. In the past everything from tin, and mercury, and silver were used to coat the backside of glass. That silver was used is likely the reason for the name "silvering." Today's process uses aluminum.

But the glass must be very clean prior to the silvering process.

If it isn't clean the aluminum oxide will not stick.

This house is 10 months old, and we were doing a one-year warranty inspection.

Many builders have the one-year warranty expire in 11 months (go figure), so this client, for whom I did a pre-drywall and final walk-through inspection, had me back to do the warranty inspection.

This mirror is in the hall bathroom that the children use.

The silvering was failing in many places along the lower edge.

The stains all looked fairly uniform, like you see in the photo. What does that mean?

I don't know - tape residue on the glass had not been completely removed, or perhaps it had the silvering damaged in some way prior to installation.

But mirrors should last a long time, and certainly longer than 10 months!

My recommendation: there is nothing typically found during any home inspection. And certainly the same defects don't show up on a one-year warranty inspection from house to house. Every house is different! So they all need a thorough going through. When things like this are found they are noted. The mirror's defect here is not the builder's fault, obviously, but now it becomes the builder's problem. Hopefully it can be returned to the supplier for a manufacturer refund. This is an unusual defect to find on a home inspection, from my experience. But a defect nonetheless!